Photo-thermographic process and element



July 9, 1968 H. c. YUTZY ET AL 3,392,020

PHOTO-THERMOGRAPHIC PROCESS AND ELEMENT Filed Feb. 8, 1965 2 SILVER HALIDE Fig.1

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EMULSION LAYER -HEAT-s ENSITIVE LAYER fsUFPORT HEAT-SENSITIVE LAYER SILVER HALIDE KEMULSION LAYER /S U PPORT l3 5 U PPORT SILVER HALIDE EMULSION BUBBLE LAYER COLORED LAYER SUPPORT Henry C. Yuizy EdwardGYackel INVENTORS ATTORNEY? United States Patent 3,392,020 PHOTO-THERMOGRAPHIC PROCESS AND ELEMENT Henry C. Yutzy and Edward C. Yackel, Rochester, N.Y.,

assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey Continuation-impart of application Ser. No. 817,846,

June 3, 1959, which is a continuation-in-part 'of application Ser. No. 584,554, May 14, 1956. This application Feb. 8, 1965, Ser. No. 440,045

12 Claims. (Cl. 96-67) ABSTRACT OF THE DISCLOSURE This invention relates to duplicating and copying materials and methods utilizing heat-sensitive and silver halide light-sensitive copy sheets.

This invention relates to duplicating and copying materials and various methods for processing such materials embodying the advantages of photography and thermography.

This application is a continuation-in-part of US. application Ser. No. 817,846 filed June 3, 1959, now abandoned which in turn was a continuation-in-part of US. application Ser. No. 584,554 filed May 14, 1956, now abandoned.

Known thermographic copying materials and methods employ heat-sensitive materials that produce a direct positive image of an original document by means of exposure of such materials to an imagewise heat pattern. Such thermographic processes have the advantage that they do not require wet processing, but they have the disadvantage that materials ordinarily used no not have copying versatility that photographic systems have. An object of the present invention is to provide a photosensitive thermographic element that can be first activated imagewise by photoexposure to produce a photographic image that is capable of forming an imagewise heat pattern by differential absorption of radiant energy. The photographic image can then be visibly intensified or permanized by thermographic process employing a separate and distinct heat'sensitive color-forming reactant incorporated in the element. Novel copying materials and methods according to the present invention have the advantage that the element is photosensitive so that original image formation can be made by photographic exposure and the advantage that the photographically-produced image can be visibly intensified by thermographic process. The invention is especially useful in intensifying and permanizing weak or unstable images produced by photography.

In a preferred embodiment of the invention we employ a sensitive element which comprises a photosensitive image-forming component such as silver halide or other photosensitive metal salt that will develop an infrared-absorbing metal image by imagewise reduction during or after photoexposure. The photographic image development may be spontaneous as in photographic print-out materials or may be developed by further processing after exposure. Sensitive elements useful according to our invention also contain a heat-sensitive image-forming reactant, separate and distinct from the photosensitive components. This reactant undergoes a visible color change when heated above a certain minimum temperature, usually at a temperature well above 50 C. As examples of copying materials suitable for use in our invention, reference is made to FIGS. 1-4 of the accompanying drawing, details of which are disclosed below.

The term original is used herein to mean an original scene or record or a copy of such scene or record of which the duplicating sheets of our invention make a "ice In a preferred embodiment of our invention we employ as the photosensitive layer a photographic silver halide emulsion containing a low concentration of silver halide. The concentration may be much below the minimum concentration necessary to produce a full density photographic image in conventional photographic films and papers. For example, we may employ silver halide emulsions containing 1 mole of silver halide for about 2,000 to' 850,000 square feet of emulsion surface. The need for development of only a minimal density photographic image provides the advantage that processing of the silver halide emulsion layer can frequently be simplified. When using emulsions of extremely low silver concentration, it is possible to produce a useable distinct image on the photothermographic element without need for fixing or Washing after development, as is necessary in conventional photography. At such low concentration, the residual silver halide will produce only a tolerable minimum of background fog.

In certain embodiments of the invention, we may incorporate both the photosensitive and the heat-sensitive components of the element in a single layer coated on a supporting surface such as paper, cellulose ester film, polyvinyl resin film, polyester films, etc. In other embodiments, the photosensitive component and the heat-sensitive component may be incorporated in separate layers which are in heateconductive contact on a support. Using this arrangement in various embodiments, either the photo-sensitive coating or the heat-sensitive coating may be outermost from the support.

The photosensitive material may be photoconductive, insulating layer of the kind used in electrophotographic elements intended for use in the Electrofax electrophotography process or in the electrolytic Photocon process. A layer of heat-sensitive image-forming material is coated over the photoconductive insulating coating. This element is first exposed photographically to produce a photoconductive image in the photoconductive insulating coating and the photoconductive image is developed to a visible image by electrophotographic development or by electrolytic development to produce a radiation absorbing image. This image is then intensified by thermographic means to intensify the xerographic image with a thermo-- graphic image.

Heat-sensitive coatings useful in our invention may comprise any of several materials which have previously been described for producing, by means of a heat pattern, a visibly distinct image in the coating. The thermographic image may be produced by means of a direct visible color change induced by heat or may be produced by means of a heat-induced chemical change which is then further developed by chemical treatment such as a coupling reaction to finally produce a visible image. A thermographic image can be produced without chemical change, as by a physical change such as melting which may result in exposure of a color layer lying beneath a heat-sensitive coating, for example. In the present invention we prefer to employ a heat-sensitive reactant that will undergo chemical change to produce a direct visible color change, although we may use other thermographic image-forming materials.

The heat-sensitive reactant used in our invention must be substantially unaffected by radiant energy, including infrared, so that the element can be exposed over its entire area to radiant energy without causing color change except in those areas heated by the radiation absorbent photographic image previously produced by means of the photosensitive component.

It is, therefore, apparent that heat-sensitive reactants useful in our invention may undergo any one of the following changes:

(1) A substantial immediate color change which gives an increase in maximum density and contrast, or

(2) Chemical decomposition leaving heat-sensitive material which can be further reacted chemically to produce.

a visible change, or

(3) Physical change, e.g., melting to reveal a colored under-layer, or, if the heat-sensitive material itself is colored, it can be made to diffuse into a fibrous support so that an image can be seen on the reverse side of the support.

Heat-sensitive reactants that undergo immediate color change usually will comprise a mixture of two components, one of which melts at a temperature within the range of about 55-125 C. and reacts with a second component to cause a color change. Miller U.S. Patents 2,663,6537, patented Dec. 22, 1953, describe heat-sensitive materials which comprise a heavy metal salt of a high molecular weight fatty acid in combination with a phenolic material. The materials described in these patents are normally solid, reactive materials, of which at least one component is an electron donor and another component is an electron acceptor in contiguity with the donor. These components react in direct ion-exchange (electron-acceptor-donor reaction at room temperature when these components are mixed in a mutual solvent which permits ionization). The reaction is immediate and forms a stable, visibly-distinct, highly polarized compound which is less dissociablethan the reactive components.

U.S. Patent 2,637,657 patented May 5, 1953, to Ozals describes a heat-sensitive, image-forming material comprising lead formate and mercuric oxalate.

U.S. Patent 2,813,042 patented Nov. 12, 1957, to Gordon et al. describes another heat-sensitive material useful in our invention. This material comprises mixed thiourea and a salt of a polyvalent material such as nickel acetate.

Morrison U.S. Patent 2,681,277 patented July 15, 1954, describes still another useful heat-sensitive material useful in the invention.

Other heat-sensitive materials which do not depend upon ionization reactions are described in U.S. Patent 2,899,334 patented Mar. 1, 1959, to Crevling et al. This patent describes a nonionizable quinone such as p-quinone, with a dihydroxy benzene. The patent also describes substituted derivatives of p-quinones and dihydroxy benzenes as useful components.

Among the photosensitive metal salts useful in accordance with our invention is silver halide which may be used in a variety of photographic silver halide emulsion compositions. In addition, the emulsion coating may contain an incorporated photographic developer, such as that described in U.S. Patent 2,716,059 issued Aug. 23, 1955, to the present inventors. A separate coating may be included, contiguous to the emulsion layer, containing silver halide processing ingredients including photographic developer. In other embodiments we may use photographic metal salt emulsions that produce direct metal image printout when the emulsion is sufiiciently expose? to actinic radiation.

The photosensitive metal salt component in elements according to the present invention may be dispersed in any suitable film-forming binder such as the conventional vehicles, e.g., gelatin, albumen, polyvinyl alcohol, hydrolyzed cellulose ester, agar-agar, gum arabic, and the like. The advantage of an incorporated developer in or contiguous to the silver halide emulsion layer is that a silver image can be produced in the coating without need for an external developer, e.g., by exposing the duplicating sheet to uniform elevated temperature (below activation temperature of the heat-sensitive component) silver image might be obtained by such treatment, such an image can be subsequently intensified to suitable image density by thermographic development as described herein to produce a corresponding colored image in or to moist ammonia vapors. While only a low density the layer containing a heat-sensitive color-forming reactant. In addition to continuous coatings of the photosensitive material and the heat-sensitive material, our invention includes elements in which either or both of these components is coated as a pattern of dots or lines, similar to a half-tone or line pattern.

A photographic image may be transferred by either a colloidal stratum transfer process or a diffusion transfer process to a receiving sheet whichcomprises a heat-sensitive color-formingcoating. The transferred photographic image then can be intensified by thermographic process to form a thermographic color image corresponding to the transferred photographic image. r a

In addition to silver 'halide as the photosensitive metal salt, we may use other photosensitive heavy metal salts which produce a metal image by selective reduction in photo-exposed areas; for example, we may use photosensitive lead salts, photosensitive mercury salts and the like. See Glafkides, Photographic Chemistry, vol. 1 (English language edition) Fountain Press, London, 1951, pp. 419-430. The use of photosensitive metal salts other than silver has been restricted in photography because many of such salts have some serious drawback; for example, the photographic image formed by lead salts is unstable and will soon fade away. The present invention provides a more practical use for such unstable photosensitive salts because the photographic image can be intensified and permanized by means of the incorporated heat-sensitive reactant which forms a permanent color thermographic image corresponding to the metal image.

Following are detailed examples illustrating certain preferred embodiments of the invention.

Example 1 Five grams of ferric stearate were ball-milled in 60 cc. of a 5% solution of ethyl cellulose in ethyl alcohol. Ten cc. of this dispersion were mixed with 5 cc. of a 10% solution of gallic acid in ethyl alcohol. The resulting mixture was then coated on a suitable support, such as paper or photographic film base, and the coating dried.

A fine grain gelatino-silver-chloride emulsion was then coated over the ferric stearate-gallic acid layer at a coverage of 1 mole of silver chloride per 4000 square feet of emulsion surface. The silver chloride emulsion layer was then dried.

The copying material obtained immediately above was then exposed to a line image using white light. A faint, print-out image was obtained without wet development. The copying material was then run through a thermographic copying apparatus of the type described in Miller U.S. Patent 2,740,895, issued Apr. 3, 1956. The original print-out image was significantly intensified by the imageobtained in the underlying heat-sensitive layer.

Example 2 image in the area of the silver image.

Example 3 The photothermographic element prepared as described in Example 2 was exposed and developed by swabbing with dilute sodium carbonate solution to obtain a silver image in the emulsion layer. Subsequent exposure of the I element to infrared radiations increased the density of the image in the region of the silver image.

Example 4 The element prepared and processed as described in Example 2 was then rinsed in warm water to remove the emulsion layer containing the silver image, leaving an image in the heat-sensitive layer. This example illustrates a preferred practice when the silver halide emulsion has been applied over the heat-sensitive layer, of finally removing the residual silver halide to prevent it from eventually printing-out and obscuring the image in the heatsensitive layer.

If desired, the silver halide emulsion layer can be applied to the support, such as paper, followed by a nontransparent (to visible light) heat-sensitive layer as shown in the following examples, with the result that the residual silver halide in the emulsion layer need not be removed after formation of the image in the heat-sensitive layer.

Example 5 A direct-positive silver halide emulsion prepared as described in Kendall et al. U.S. Patent 2,541,472, issued Feb. 13, 1951, was coated on a paper support, exposed to an image and developed in a paper developing solution to obtain a direct-positive silver image in the emulsion layer. Thereafter the emulsion layer was coated with a dispersion of heat-sensitive ingredients prepared as follows:

Five grams of ferric stearate were milled into 60 cc. of a 6% solution of ethyl cellulose in ethyl alcohol. Ten cc. of this composition were mixed with 5 cc. of a solution of gallic acid in ethyl alcohol. This coating thus applied to the emulsion layer obscured the silver image therein. When the element was then subjected to infrared radiations, a positive image corresponding to the silver image in the underlying emulsion layer appeared in the outer heat-sensitive layer. When the element was then subjected to prolonged white light exposure no appreciable printout image was visible in the underlying emulsion layer.

If desired, the procedure of this example can be varied by applying both the silver halide emulsion layer and the heat-sensitive layer to the support prior to image exposure. Thereafter, the silver image is developed in the emulsion layer followed by the infrared exposure.

Example 6 The following composition was prepared:

Twelve grams of ferric stearate were milled in a solution of 5 grams of ethyl cellulose in 70 cc. of ethyl alcohol. Ten cc. of this composition were mixed with 10 cc. of a 4% solution of gallic acid in ethyl alcohol.

A paper support was coated with a direct-positive silver halide emulsion as in Example 5, except that the emulsion contained the silver halide developing agent, 4-phenyl catechol, followed by a coating of the ferric stearate-gallic acid composition described immediately above.

The resulting element was exposed to an image and a direct-positive silver image developed in the emulsion layer by wetting the paper support with 2% sodium hydroxide solution. Infrared exposure of the element produced an image in the heat-sensitive layer corresponding to the underlying silver image.

Example 7 An aqueous gelatin solution contatining hydroquinone and N-methyl-p-aminophenol sulfate developing agents, as well as sodium sulfite, sodium carbonate and potassium bromide was coated on a conventional paper support at a coverage of approximately 10 grams of solution per square foot. Over the gelatin layer was coated an ordinary fine-grain silver bromiodide emulsion. The emulsion was coated at an approximate silver coverage of 1 mole of silver bromiodide per 37,000 square feet of emulsion surface.

A dispersion of 2-n-hexadecyl-S-methylhydroquinone and 2-n-hexadecyl-5-methylquinone in aqueous gelatin was prepared and the dispersion was coated over the above emulsion layer at an approximate concentration of 0.2 gram of the hydroquinone compound and 0.2 gram of the quinone compound per square foot of surface.

The resulting copying materialwas then dried and exposed to a line image using daylight quality radiation. It was then developed at 70 C. for 10 seconds, at a relative humidity of The damp copying material was dried for one minute with an ordinary hair drier. At this point, Only a faint silver image could be seen. The dried copying material was then exposed uniformly to infrared radiation in an apparatus of the type described in US. Patent 2,740,895. The faint silver image was markedly intensified by the blue image resulting from the thermographic exposure. The resulting print had a high image D and low background D After exposing to bright room light or sunlight for several hours, the processed material showed no decrease in D and only very slight increase in D Example 8.An element containing the thermographic reactants and silver halide in the same layer (1) Preparation of the thermographic reactant dispersions (A) Quinone dispersion.-Fifty grams of 2-n-hexadecyl-S-methyl-p-quinone were dissolved in 250 cc. of chloroform. This solution was then added to 500 grams of a 10% aqueous solution, to which had been added 250 cc. of a 5% aqueous solution of sodium isobutylnaphthalene sulfonate. This mixture was then passed through a colloid mill.

(B) Hydroquinone dispersi0n.Ten grams of 2,5-din-octyl hydroquinone were dissolved in 50 cc. of butyl alcohol. This solution was then added to 100 grams of a 10% aqueous gelatin solution, to which had been added 50 cc. of a 5% aqueous solution of sodium isobutylnaphthalene sulfonate. This mixture was passed several times through a colloid mill.

Each dispersion was chill-set, noodled and dried, removing the volatile solvents. Twelve grams of dispersion A were redispersed in 100 cc. of water, and 16 grams of dispersion B were redispersed in a second 100 cc. of water.

(2) Preparation of coating The above two dispersions were then combined with 1 gram of a gelatino-silver-chloride emulsion. The resulting mixture was coated on a cellulose acetate support at an approximate coverage of 1 mole of silver chloride per 2500 square feet of emulsion surface. The coating was then dried.

The dried coating was then exposed for 1 second to 25-watt tungsten illumination through a line negative, a 0.3 step tablet or a 015 step tablet. The separately exposed strips were then developed for 1 minute ina developer having the following composition:

7 Grams Elon developing agent 2.0 Sodium sulfite, desiccated 90.0 Hydroquinone 8.0 Sodium carbonate, monohydrated 52.5 Potassium bromide 5.0

Cold water to make 1.0 liter.

The developed print was then fixed for 3 minutes in hypo, washed in water and dried.

Only a faint silver image could be seen after the above photographic development, but passage of the copying material through a printing machine of the type shown in US. Patent 2,740,895, resulted in marked intensitication of the silver image by a blue image having high max- 7 Example 9 Aqueous gelatin dispersions of 2-n-hexadecyl-5-methylhydroquinone and Z-n-hexadecyl-S-methylquinone were prepared as described in Example 8 above, except that slightly larger quantities of gelatin were'used. These dispersions were mixed and coated on an acetate film support at the following approximate coverage:

Mg./square feet Hydroquinone compound 368 Quinone compound 492 Gelatin 469 Over the thermographic layer was coated a coarsegrained, gelatino-silver-bromiodide emulsion of the type commonly used in screen-light, medical X-ray films. This emulsion was coated at an approximate silver cover of 563 mg. of silver per square foot.

The above copying material was then dried and exposed on an Eastman Type 1B Sensitometer to a 100-watt light source emitting daylight quality radiation, for second. The exposed copying material was then processed in the usual manner in a conventional X-ray developer, fixed, washed and dried. The processed copying material was then passed twice through a printing machine of the type described in US. Patent 2,740,895. The copying material had a relative speed of 100, a gamma of 1.39 and gross fog of .48 before intensification, and a relative speed of 257, a gamma of 4.25 and gross fog of .49 after intensification in the printing machine.

Example 10 An ortho-sensitized, high-contrast, gelatino-silver-chlorobromide emulsion of the type used in graphic arts films, was coated on a thermographic layer prepared as described in Example 9 above. The emulsion coating contained 1 mole of silver halide per 200 square feet of emulsion surface The copying material was then exposed on an Eastman Type 1B Sensitometer for 1 second and processed for 2% minutes in a conventional graphic arts developer. The material was then fixed, washed and dried.

The processed material contained only a faint silver image which was markedly intensified by passage through a printing machine of the type used in Example 9. The copying material had a relative speed of 100, a gamma of 4.5 and gross fog of .44 before infrared intensification and a relative speed of 151, a gamma of 7.3 and gross fog of .44 after intensification by exposure to infrared radiation, as described above.

Example 11 Grams N-methyl-p-aminophenol sulfate 0.3 Hydroquinone 6.0 Sodium sulfite (des) 38.0 Sodium bisulfite 1.5 Sodium carbonate monohydrate 22.0 Sodium bromide 0.78 Citric acid 0.7

Water to make 1 liter.

The developed copying material was then fixed with hypo in the usual manner, washed and dried. The processed film contained an ordinary silver image which was markedly intensified by an exposure to infrared radiation by passage through a printing machine of the type used in Example 9. The processed film had a relative speed of 100, gamma of 2.88 and gross fog of .44 before intensification and a relative speed of 289, a gamma of 2.98 and gross fog of .48 after intensification.

Example 12.-Therm0graphic intensification of a solvent-transferred image Nuclei and tlzermographic components coated in the same layer A. Nuclei-thermographic layer (1) Fifty grams of 2-hexadecyl-5-methylquinone were dissolved in 250 cc. of chloroform. This solution was added to 500 grams of a 10% aqueous gelatin solution to which had been added 250 cc. of a 5% aqueous'solution of sodium isobutylnaphthalene sulfonate. This mixture was passed through a colloid mill.

(2) Ten grams of di-octyl-hydroquinone. were dissolved in 50 cc. of butyl alcohol. This solution was added to grams of a 10% gelatin solution to which had been added 50 cc. of a 5% aqueous solution of sodium isobutylnaphthalene sulfonate. The mixture was passed through a colloid mill.

Each dispersion was chill-set, noodled, and dried, removing the volatile solvents. Twelve grams of (1) were redispersed in 100 cc. of water and 16 grams of (2) were redispersed in a second 100 cc. of water.

The following materials were mixed together and coated on a cellulose acetate support at a .00'6-inch knife setting:

Cc. Dispersion (1) 25 Dispersion (2) 20 Zinc sulfide (.002 N) nuclei dispersion 5 Saponin solution (15% aqueous) 3 Formaldehyde solution (aqueous 10%) 0.5

B. Emulsion layer Over the nuclei-thermographic layer was coated a silver chloride emulsion dispersed in cellulose ether phthalate. The emulsion was hand coated at a .006-inch knife setting and dried.

Exposure and processing infrared printing machine of the type used in Example 9. A marked intensification of the weak silver image occurred.

In the areas 'where silver had been deposited, the infrared exposure intensified the image by forming a colored quinhydrone.

Example 13.-Therm0graphic intensification of a solvent transferred image Nuclei and thermographic components coated in separate layers A. Thermographic layer The following materials were mixed together, hand coated on a cellulose acetate film support at a knife setting of .004-inch and dried:

B. Nuclei layer Over the thermographic layer was coated a dispersion of zinc sulfide and gelatin at a knife setting of .004-inch and dried.

C. Silver halide emulsion layer Over the zinc sulfide nuclei layer was coated a silver chloride-cellulose ether phthalate emulsion (see Talbot et al. US. Patent 2,725,293, issued Nov. 29, 1955) at a knife setting of .006-inch and dried.

Exposure and processing A sample of the above three-layer coating was exposed and processed the same as described in Example 12. The processed film containing the transferred silver image was intensified by passing through an infrared printing machine of the type used in Example 9 above. The silver image was intensified as described in Example 12 above.

Example 14 A light-weight paper stock was coated with the photographic developing composition described in Example 7 and the dried developer coating was then overcoated with a thermographic composition comprising 2,5-di-n-octylhydroquinone and 2-n-hexadecyl-S-methylquinone. The hydroquinone-quinone dispersion was made by first dispersing the hydroquinone compound in butyl alcohol and dispersing this solution in gelatin -by means of a colloid mill. The gelatin dispersion was dried, evaporating the butyl alcohol.

In a similar manner, a dispersion of the quinone compound was dissolved in chloroform and aqueous gelatin solution. This dispersion was also dried, evaporating the chloroform.

A sample of the hydroquinone dispersion and the quinone dispersion was redispersed in water and the two dispersions blended. To the mixed dispersion was added a small amount of the silver halide emulsion referred to in Example 8. This gave a coating with a silver coverage of approximately 1 mole of silver per 140,000 square feet of emulsion surface, and a coverage of approximately 275 mg. of the quinone compound per square foot and approximately 210 mg. of the hydroquinone compound per square foot.

This paper was then dried and exposed in the customary manner to a line image using daylight quality radiation. The treated paper was developed for seconds in an atmosphere of air saturated with water vapor at 60 C., whereupon a silver image of low density appeared. The silver image was then intensified by passing the paper through a printing machine of the type described in Example 9, using infrared radiation.

Example ]5.Ferric stearate pyrrogallol thermographic system Reactant A: dispersed 50 grams of ferric stearate in 200 ml. of denatured ethanol by ball milling for 24 hours.

Reactant B: dissolved 150 grams of hexamethylenetetramine in 1200 ml. of denatured ethanol at 65 C. and added this solution with good stirring to 200 grams of pyrrogallol dissolved in 400 ml. of denatured ethanol at 65 C. After cooling to C. with stirring, the crystalline precipitate was removed by filtration, washed with ethanol, and dried. Dispersed 50 grams of the dry powder in 150 ml. of denatured ethanol by ball milling for 24 hours.

Ractant C: dissolved 1 gram of oxalic acid in 10 ml. of ethanol.

Binder: dissolved 5 grams of ethyl cellulose in 100 grams of ethanol.

Composition of the thermographic material:

Reactant A 50 Reactant B l0 Reactant C 4 Binder 20 The ingredients in the thermographic composition were thoroughly mixed and then hand-coated on a light-weight paper stock to a thickness of approximately 3 mils and allowed to dry at room temperature. The dried coating was then overcoated with additional binder solution and again dried. The coated paper was then wet with a 5% solution of a polyalkylene oxide wetting agent (Tween in ethanol and again dried. The dried coating was then overcoated with a gelatino-silver-chloride emulsion at a silver coverage of 1 mole of silver per 35,000 square feet.

The emulsion coating was then dried and exposed in the usual manner to daylight quality radiation through a line image. The exposed material was then treated for 10 seconds with an ordinary photographic developing solution and then dried in air. Only a weak silver image appeared and this was intensified by passing through a printing machine of the type described in Example 9, using infrared radiation.

Example 16.Nickel acetate tetrahydrate-calcium sulfide thermographic system Reactant A: dispersed grams of nickel acetate tetrahydrate in 250 ml. of anhydrous butyl acetate by ball milling for 24 hours.

Reactant B: dispersed 56 grams of calcium sulfide in ml. of anhydrous butyl acetate by ball milling for 24 hours.

Binder: dissolved 5 grams of ethyl cellulose in 100 grams of anhydrous butyl acetate.

Composition of the thermographic material:

Reactant A 10 Reactant B 5 Binder 15 The above thermographic composition was thoroughly mixed and hand-coated onto light-weight paper stock at a thickness of approximately 3 mils. The coating was then dried at room temperature, overcoated with additional binder solution and again dried. The binder coating was overcoated with a 5% solution of bis phenol polycarbonate resin (see SchnellAngew. Chem, vol. 68, pages 633-60), dissolved in chloroform and then dried. The polycarbonate resin layer was overcoated with a second bis phenol polycarbonate resin layer and dried, overcoated with a 5% solution of a polyethylene oxide wetting agent (Tween 80) and butyl alcohol and dried.

The heat-sensitive layer was then overcoated with a conventional silver halide emulsion of the type described in Example 15, giving a pale green colored coating. This coating was dried, exposed to daylight quality radiation through a line image and developed by swab development as described in Example 15. Only a faint silver image appeared, but this was intensified by passage of the duplicating sheet through a printing machine of the type described in Example 9 above, using infrared radiation. An intense black image appeared.

Example 17.C0pper stearate-diphenylcarbazone thermographic system Copper stearate was dissolved in 5 parts of heptane and 5 parts of diphenyl carbazone were dispersed in 5 parts of butyl acetate (in which the carbazone is partially soluble). The diphenylcarbazone solution was then coated onto light-weight paper stock and dried. The paper stock was then coated with the copper stearate dispersion and again dried to give a material having pink-tan color. The thermographic layers were then overcoated with a conventional silver halide emulsion as described in Example 15, which was exposed and developed as described in that example. An image having low silver density appeared, but this was intensified to a strong purple image by passage through a printing machine of the type described in Example 9, using infrared radiation.

1 1 Example 18.Zinc stearate-diphenylcarbazone thermographic systemv Zinc stearate was substituted for the copper stearate in Example 17 to yield a thermographic paper having a slight pink color when butyl acetate was used as the vehicle for the carbazone. Substitution of heptane as the vehicle for the carbazone gave a colorless paper. The thermographic layers were given an overcoating with a silver halide emulsion layer as described in Example 15. The silver halide emulsion was then exposed and processed as described in Example 15. Only a weak silver image appeared, but this was intensified to a scarlet image by passage of the treated paper through a printing machine of the type described in Example 9, using infrared radiation.

Paper coated With the carbazone using butyl acetate as a solvent had a slightly pink background but gave a more intense image than coatings using carbazone coated from heptane.

Example 1 9.-Multilayer thermographic coating One side of a low-shrinkage, clear support was coated with a blue-sensitive silver chlorobromide emulsion containing thermographic reactants which, upon heating, form a blue color. The thermographic reactants were added to the emulsion in the form of a dispersion prepared as follows:

Dispersion A:

2,5-di-n-octyl hydroquinone gm 140 fl-Butoxy-p-ethoxyethyl acetate ml 700 Gelatin solution (10% aqueous) gm 1400 Sodium isobutylnaphthalene sulfonate solution (7.5% aqueous) ml 14 2,5-di-n-octylquinone r gm 25 fl-Butoxy-fi-ethoxyethyl acetate ml 125 Gelatin solution (10% aqueous) gm 250 Sodium isobutylnaphthalene-sulfonate solution (7.5%

' aqueous) ml 20 Distilled water ml 100 The compounds were dispersed and put through a colload mill five times at 95 C. This dispersion was then chill-set, noodled and washed in chilled water for 12 hours. It was then redispersed and made up to a total weight of 3300 gm.

Also added to the emulsion were 300 ml. of a 15% solution of saponin as a coating aid and 90 ml. of a 10% solution of formaldehyde as a hardener. All of these additions brought the total weight of the emulsion to 8840 gm./mole Ag. The emulsion was coated at a thickness of .004" which yielded the following coverages:

Silver, .110 gm./sq. ft.; 2,5 di n octylhydroquinone, .153 gm./sq. ft.; 2,5-dinoctylquinne, .205 gm./sq. ft.

The film was suitably dried. The reverse side was coated with a red-sensitive chlorobromide emulsion containing thermographic reagents identical to those contained in the blue-sensitive layer described previously. The red-sensitive emulsion had a higher mole weight than the blue-sensitive emulsion so that the weight of the emulsion plus the thermographic reactants, etc., came out to be 9960 g./mole Ag. The emulsion was coated under the same conditions as the first one but, being slightly more diluted yielded these coverages:

Silver, .0978 gm./sq. ft.; 2,5-di-n-octylhydroquinone, .135 gut/sq. ft; 2,5-di-n-octylquinone, .180 gn1./sq. it.

The film was again suitably dried. The dried, doublecoated product, containing a high blue-sensitive emulsion layer on one side and a high red-sensitive emulsion layer on the opposite side of the support, was then given an imagewise exposure. The exposure for the differentially sensitized emulsion layers was accomplished by utilizing two variable density step-wedges side-by-side with a Wratten No. 29 light filter (to yield the red-light exposure) over one step-wedge and a Wratten No. 48 lighter filter (to yield the blue-light exposure) over the other. The film was exposed to a 15-watt bulb at a distance of 15 inches. The exposed film was then developed for 2 minutes in the developer used in Example 8, fixed, washed and dried. Two weak images, side-by-side, were evident on the processed film strip. One image was present in the blue-sensitive layer, corresponding to the blue-light exposure, and one on the reverse side of the film in the red-sensitive layer corresponding to the red-light exposure. The film was then subjected to heat (infrared) radiation in a printing machine of the type described in Example 9. It was observed that an intensified (higher density) image was obtained in the light exposed areas of the film. To prove that the intensified images present on the film were composed of single images on two sides of the support and not simply overlapping images, a minute portion of the density step of each image was scraped. Where the steps were scraped, clear support was visible rather than the presence of another image. Of course in practice, thermographic reactants forming two different colors could be used.

Example 20.Silver behenate thermographic system A dispersion was prepared by ball milling for 24 hours, 9 g. (0.02 mole) silver behenate, 6.8 g. (0.02 mole) behenic acid, 3 g. polystyrene, and 81.2 g. anhydrous ethyl acetate. A solution was prepared by dissolving 6.2 g. (0.04 mole) rotocatechuic acid, 8 g. diphenyl phthalate, 0.4 g. citric acid, and 0.4 g. phthalic anhydride in g. anhydrous ethyl acetate. A coating mixture was prepared by mixing 50 g. of the dispersion and 30 g. of the above solution with 40 g. of ethyl acetate. This mixture was machine coated on paper stock at a coverage of about 6.5-7 g. per square foot. The coated sheet was overcoated with a 2% solution of polystyrene in ethyl acetate at a coverage of about 4 g. of the solution per square foot. Next a coating of 10.4 g. of Dow 512K latex (a styrenebutadiene latex), diluted to g. with water was coated at a spread of about 4 g. per square foot. The coated sheet was finally coated with the silver halide emulsion of Example 15. Exposure and development as described in Example 15 gave an image of low density which was intensified to a black image by passing the sheet through a printing machine of the type used in Example 9.

Example 21 .Diaz0 tlzermographic system A fine-grain positive photographic film was exposed to two step-wedges and processed for 5 minutes in the developer described in Example 11 above, fixed with hypo, washed and dried. This film was then bathed for 2 minutes in a /2% solution of the zinc chloride salt of p-biphenyldiazonium chloride. Without drying, one stepwedge image was exposed to a General Electric Industrial Reflector or Infrared Lamp for 15 seconds at 4 inches, While the second step-wedge image was left unexposed to the infrared radiation. Both portions of the film were then bathed in an alkaline solution containing B-naphthol and phloroglucinol for 2 minutes. The film was then treated for 5 minutes in a bleach bath having the followmg composition:

Grams Potassium ferricyanate 100 Potassium bromide 10 Borax 7.5 Boric acid 50 Water to make 1 liter.

The film was then rinsed for 2 minutes in running water and fixed in a conventional photographic fixing bath containing hypo. It was again washed for 3 minutes in water and dried.

The strip which Was exposed by the infrared lamp did not show any colored image where the silver image had been, although the remaining part of the strip was colored deep orange.

The strip which had received no infrared radiation was over-all orange in color. Since the only difierence in the treatment of the two strips was the infrared exposure, the results showed that the diazonium salt was destroyed by localized heating in the areas containing the silver image. A similar experiment, carried out with a drying step before the infrared exposure, gave a similar result.

Example 22 Example 21 was repeated, except that 2,2'-dimethoxybenzidene tetrazonium chloride-zinc chloride double salt was employed in place of the diazonium salt used in Example 21. The image produced in this case upon treatment as described in Example 21 was magenta in color. This magenta dye image was positive with respect to the original subject.

It has also been found that heat-intensification can be used to produce a copy by means of diazo compounds which do not undergo decomposition upon exposure to heat of the degree required to melt a low-melting polymer. For this technique, a diazo compound and a coupling component are separately dispersed in a polymer solution in which both the diazo compound and coupler form colloidal dispersions. The two dispersions are then coated on a paper support and dried. The coated sheet can then be exposed by transmitted or reflected light of high intensity in contact with a line original. The light parts of the original transmit or reflect the light (usually ultraviolet light) to the copy sheet and decompose the diazo compound locally. The dark parts of the original absorb the incident radiation, causing an increase in the temperature of the copying sheet in contact with them. This increase in temperature is sufiicient to melt the polymer and allow the diazo compound and coupler to flow together, yet the temperature does not reach a degree sufficient to decompose the diazo compound, as in the case of Examples 21 and 22 above. The exposure decomposing the diazo compound and the exposure producing the melting of the polymer can be carried out separately or simultaneously depending upon the spectral distribution of the light source. With a light source of suitable intensity and spectral distribution, suitable relative amounts of ultraviolet and total radiation (including infrared components), both the photochemical decomposition of the diazo compound and the thermal effect resulting in coupling can be carried out at the same time and with the same exposure.

Example 23.Thermgraphic system using physical change Paper stock containing a black pigment or dye was coated with a blushed baryta layer containing a clear film-forming material, such as cellulose acetate, ethyl cellulose, etc. Over the blushed baryta layer was coated an ordinary silver halide emulsion at a low silver coverage, such as 1 mole of silver per 35,000 square feet of emulsion surface. The paper was then dried and exposed to a line image. Upon development with a conventional silver halide developing agent, such as described in Example 11, a faint silver image having poor maximum density and contrast appeared. However, upon exposure of the paper in a printing machine of the type described in Example 9 above, the image areas in the photographic emulsion absorb suificient heat in proportion to their silver densities, causing the baryta bubbles directly under such areas to collapse into a clear film, allowing the black of the raw stock to show through. This produced a marked intensification of the silver image. Exposure of the paper in the non-image areas merely caused reflections in those areas with no visible change occurring.

Example 24.Intensificati0n of plzotoconduclographic image A zinc oxide photoconductographic composition was coated on a conventional paper-backed aluminum foil according to known techniques. Over the zinc oxide material, which was dispersed in a conventional insulating binder, such as a butadiene-styrene copolymer, was coated a gelatin thermographic layer prepared as described in Example 7, except that the thermographic composition contained a small amount of sodium chloride in order to increase conductivity.

The photoconductographic material was then exposed to a line image in the ordinary manner and developed with a swab saturated with a silver chloride-hypho developer. A potential of about 70 volts positive was applied between the aluminum backing and the development swab during the developing operation. Only a weak image appeared. The copying material was dried and then put through a thermographic printer of the type described in Example 9 using infrared radiation. The weak silver image was markedly intensified by development of a purple image in the thermographic coating.

B with stirring. To this solution were then added 312 ml. of water and 6 ml. of a 20% formaldehyde solution. This developer composition was then coated on two strips of a single-weight paper base at a coverage of approximately 10.00 gm./sq. ft.

The dried developer coatings were then overcoated with a photographic-thermographic composition comprising 2,S-di-n-octylhydroquinone and 2,5-di-n-octylquinone dispersed in gelatin. The quinone-hydroquinone dispersion was made by first dispersing the 2,5-di-n-octylhydroquinone in B-butoxy-B-ethoxyethyl acetate and dispersing the solution in gelatin by means of a colloid mill. The gelatin dispersion was then chill-set, shredded into small particles and washed in constantly moving chilled water for 12 hours. The water was then drained otf and the hydroquinone dispersion was collected and dried. The 2,5-di-noctylquinone was dispersed, washed and dried in a similar manner. A sample of each dispersion was redispersed in water and the two dispersions blended, giving a mixed dispersion of the quinone and the hydroquinone. Small amounts of a gelatino-silver-bromoiodide emulsion were added to two aliquot samples of the quinone-hydroquinone dispersion and these compositions were then coated over the separate strips of the dried developer layers obtained previously on single-weight paper base.

15 16 The coatings made yielded the following coating data: 0.002" wet thickness. Photographic exposure produced a Coating Sq. ft. Sq. ft. Mg. Mg. Mg. Mg. Number coated co-ited/ Quinone/ Hydroqui- Ag/Sq. Get/Sq.

mole Ag sq. ft. none/sq. it. it. it.

The above coatings were then exposed to a line image using daylight quality radiation and developed for seconds in an atmosphere of air saturated with water vapor at 60 C. Little or no developed density appeared in either of the coatings. However, exposure of the dried coatings to infrared radiation in the manner described in Example 9 produced a satisfactory blue image in both coatings.

Example 26 A light-sensitive lead iodide coating was prepared as follows: A light-sensitive lead iodide coating was prepared by adding 100 ml. of /2 molar lead nitrate solution to 200 ml. of /2 molar potassium iodide solution. The supernatant liquid was decanted and the precipitate was then dispersed in 1,000 ml. of 10% gelatin solution. One-hundred ml. of 1% sodium thiosulfate solution was added and the mixture was heated at 45 C. for 30 minutes. After cooling, 10 ml. of glycerol was stirred into 250 ml. of the emulsion and the dispersion was then ready for coating. A dispersion of thermographic reactants, 2,5-di-n-octylhydroquinone and 2,5-di-n-octylquinone was prepared as described in Example 19 and the dispersion was coated at a concentration of 186 mg. of the quinone and 140 mg. of the hydroquinone on a paper support and dried. The photographic lead iodide emulsion prepared as described above was then coated over the thermographic layer. Two samples were made, one containing a spread of 1 mole lead per 700 square feet and another containing a spread of 1 mole lead per 1400 square feet. The finished samples were prepared as described above exposed for four minutes to direct sunlight through a transparent original. Lead iodide printed out in both samples to form a metallic lead image which was then intensified by passing the element through a Thermofax Secretary thermographic copying machine. Density of the printed-out lead image was considerably intensified by the thermographic image which remained after the lead image had faded with time.

Example 27 A dispersion of heat-sensitive, thermographic compounds, 2,5-di-n-octylquinone and 2,5 di-n-octylhydroquinone was prepared in gelatin as described in Example 19 above. The dispersion was coated at a coverage of 186 ml. octylquinone per square foot and 140 ml. hydroquinone per square foot on a paper support. A photosensitive mercury salt emulsion was prepared as follows. Under red safelights in 400 ml. water containing 4.0 ml. concentration nitric acid were dissolved 25 g. of mercurous nitrate. To this solution was added dropwise -a solution containing 10 g. of potassium iodide in 20 ml. water. A yellow precipiate resulted which was washed 3 times by decantation. A slurry of this precipitate was added to 250 ml. of 10% gelatin solution and water was added to make 300 ml. This mixture was then pumped through a hand operated homogenizer three times to disperse the precipitate in the emulsion. Five ml. of 1 /2% saponin solution was added to the emulsion and coatings were made over the thermographic coating described above at 0.004 wet thickness. A control coating was made on paper stock without the thermographic coating. Photoflood exposures of the photosensitive coatings produce a print-out image after 12 seconds of exposure. Thinner coatings were made by diluting the stock emulsion as follows: to 10 ml. of 10% gelatin solution were added respectively 1.0 ml., 0.1 mL, portions of the stock emulsion described above. These diluted emulsions were coated at much weaker print-out image which could be intensified by thermographic exposure in a Thermofax' Secretary thermographic copying machine;

Example 28 An aqueous dispersion of 5-(w-carboxypentyl)toluqui none (1.77 ml. of 10% dispersion) was mixed with a ball milled aqueous dispersion of 5 (w-ca'rboxyprop-yl) noctylhydroquinone (7.75 ml. of 4% dispersion). To this mixture was added 1.20 g. of aqueous 10% gelatin solution, 1.80 ml. of Titanox-AWD titanium dioxide dispersion in water (500 mg./ml.), one drop of 1 N sulfuric acid, 0.136 g. CuSO 0.40 ml. of a 15.3% solution of saponin and 0.20 ml. of a 2.72 percent aqueous solution of mucochloric acid. A portion (4.2'ml.) of this warm slurry was coated at 0.002" on cellulose acetate film base. To the remaining slurry was added 0.59 g. CuSO and this new slurry was coated as before (4.2 ml. at 0.002"). A third sample was prepared using the remaining slurr-y with 0.27 g. CuSO Samples of these coatings were exposed for 5 minutes to ultra-violet light to give print-out copper images. These images are unstable and disappear after several days in roomlight. Corresponding samples were similarly exposed and then run through a Thermofax Secretary thermographic copy machine to give intensification of the image by formation of the colored quinhydrone.

In the accompanying drawing, cross sections of certain duplicating materials are shown diagrammatically.

In FIG. 1 the duplicating material comprises a support 10 coated with a heat-sensitive layer 11 which is overcoated with a photographic silver halide emulsion layer 12.

FIG. 2 shows a variation of FIG. 1 wherein a heatsensitive layer 11 is coated over a photographic silver halide emulsion 12 on a support 10. 7

FIG. 3 depicts a single sensitive layer 11 coated on a support 10. The single coating 11 comprises discrete particles of silver halide grains 14 dispersed with particles of heat-sensitive color-forming reactant 15, which may be a single compound or a mixture of compounds.

In FIG. 4 a color layer 16 is coated on a support 10. A bubble layer 17 coated on the color layer becomes transparent when the bubbles burst. A silver haiide photographic emulsion layer 18 is coated over the bubble layer.

In certain embodiments of our invention the heatsensitive layer may comprise an opaque coating which becomes transparent upon exposure to heat. This heatsensitive opaque layer is coated over a colored base and a photosensitive image-forming layer is coated over the heat-sensitive layer. After production of a photographic, infrared absorbing image in the photosensitive layer, the element is exposed to infrared radiation to heat the photographic image areas. Heat produced in the photographic image causes corresponding areas in the heat-sensitive layer to turn from opaque to transparent, revealing the support color in image areas corresponding to the photo graphic image. Examples of heat-sensitive coatings for this purpose may be a cadmium stearate-rubberasulfur' composition, a stearic acid-aluminurn-palmic-composition or a wax-silicate composition. Such opaque coating compositions, which turn transparent when exposed to heat, are described, for example, in U.S. Patent 1,783,442 patented December 2, 1930, to Mayer; U.S. Patent 2,668,- 126 patented February 2, 1954, to Taylor; and U.S. Patent 2,710,263 patented June 7, 1955, to Clark et al.

In still another embodiment of our invention a colored layer which uniformly absorbs infrared radiation is coated on a supporting surface such as paper and a photographic silver halide emulsion in coated over this layer. After development of a silver image, the coated element is exposed to infrared which causes fusion of the colored layer to the supporting surface. The overlying silver halide emulsion layer and unfused heat-sensitive coating can then be removed from the surface of the support. This technique yields an image which is negative with respect to the silver image. A useful heat-sensitive material for this purpose, containing benzophenone and a finely divided metal of carbon black is disclosed in U.S. Patent 2,629,671 issued February 24, 1953, to Murray.

In still another embodiment of our invention a colored wax layer is coated on a porous support such as paper and a photographic silver halide emulsion is coated over the wax layer. A silver image is produced in the emulsion layer which is then exposed to infrared radiation to cause imagewise heating of the silver image. In heated areas the Wax melts, permeates the porous support and forms a visible image on the reverse side of the support.

A low intensity silver image may be produced on a heat-sensitive layer coated on a support by the process known as colloid stratum transfer. By this technique, a film having a substantially unhardened photographic silver halide emulsion layer and containing in one layer a gelatintanning silver developing agent and a nontanning silver developing agent, as described in U.S. Patent 2,716,059 patented Aug. 23, 1955, to Yutzy et 'al., is exposed imagewise and then developed to produce a hardened gelatin and silver image in the emulsion layer. Unhardened gelatin, containing developed silver is then transferred from the emulsion layer to the surface of a second element by pressing the first element against the second. The transfer receiving element is coated with a layer of heatsensitive material, for example of the type described in U.S. application Ser. No. 763,248 filed May 19, 1958, by Crevling et al. A silver image is intensified by heating with infrared radiation to produce a colored image in the heat-sensitive coating corresponding to the transferred silver image.

In addition to the heat-sensitive materials already described, our invention can employ a heat-sensitive coating which undergoes change, when heated, from an extensively oriented state to a disoriented state. An imagewise, heat-caused disorientation can be viewed by means of polarized light and filters. The heat-sensitive coating may be a material whose water-ink receptivity is modified by heat, or one whose adhesive property is modified by heat (permitting development with a toning powder). Our invention comprises use of any image-forming heat-sensitive coating as described in the specification.

It will be understood that modifications and variations may be made within the scope of the invention as described above and as defined in the following claims.

We claim:

1. A duplicating sheet comprising a support and coated on one side thereof a heat-sensitive coated layer and a photosensitive coated layer, said respective layers being both coated on said support in heat transmissive contact with each other, said heat-sensitive layer consisting of a coating composition that is substantially unaffected by radiant energy including infrared radiation and that comprises a heat-sensitive reactant which is capable of producing a visible darkening in said heat-sensitive layer, in addition to visible darkening caused by photosensitive metal salt reduction, by thermographic reaction at a temperature above 55 C. and below the char temperature of the sheet, and said photosensitive layer being a photographic silver halide emulsion containing 1 mole of silver halide per 2,000 to 850,000 square feet of the coated layer.

2. A duplicating sheet comprising a support and coated on one side thereof a single coated layer of a coating composition which has dispersed therein a heat-sensitive component and a photosensitive component, said heat-sensitive component being a heat-sensitive reactant that iS capable of producing a visible darkening in said layer, in addition to visible darkening caused by photosensitive metal salt reduction, by thermographic reaction at a temperature about 35 C. and below the char temperature of said sheet and that is substantially unaffected by radiant energy including infrared radiation, and said photosensitive component being photographic silver halide dispersed in said layer at a concentration of 1 mole silver halide per 2,000 to 850,000 square feet of said coated layer.

3. The duplicating sheet defined in claim 1 wherein said heat-sensitive layer is at least partially transparent to the actinic radiation to which said photosensitive layer is sensitized and said heat-sensitive layer is coated outside said photosensitive layer on said one side of the support.

4. The duplicating sheet defined in claim 1 wherein said photosensitive layer is coated outside said heatsensitive layer on said one side of the support.

5. The duplicating sheet defined in claim 1 wherein said heat-sensitive reactant is one capable of producing a visible darkening of said heat-sensitive layer at a temperature in the range from 55 C. to C.

6. The duplicating sheet defined in claim 2 wherein said heat-sensitive reactant is one capable of producing a visible darkening of said layer at a temperature in the range from 55 C. to C.

7. The duplicating sheet defined in claim 6 wherein said coating composition further comprises a developer composition dispersed in said coating composition with developer compositions having a silver halide developer that is activatable in a liquid activatablc solution.

8. The duplicating sheet defined in claim 6 wherein said heat-sensitive reactant consists of two reactive compounds at least one of said compounds having a melting point in said temperature range, both of said compounds being dispersed in the layer with each physically distinct from the other so that on heating of said layer to said melting temperature the one compound will melt and combine with the other to produce said visible darkening.

9. The duplicating sheet defined in claim 6 wherein said two reactive compounds consist of a p-quinone compound and a dihydroxy benzene compound.

10. The duplicating sheet defined in claim 8 wherein said two reactive compounds consist of a p-quinone compound and a dihydroxy benzene compound.

11. A duplicating sheet comprising a support, a heatsensitive, light-insensitive thermographic coating and a light-sensitive silver salt coating, said silver salt coating being capable of forming infra-red absorptive silver images in the light-struck areas, said thermographic coating being capable of undergoing permanent visible change only in said light-struck areas by heat conducted through said infra-red absorptive silver images when said silver images are exposed to infra-red.

12. The duplicating sheet defined in claim 2 wherein said heat-sensitive reactant comprises silver behenate.

References Cited UNITED STATES PATENTS 2,326,012 8/1943 Dalton 96-88 2,684,341 7/1954 Anspon et al 9668 2,692,178 10/1954 Grandadam 96-1 2,798,960 7/ 1957 Moncrieff-Yeates 96-1 FOREIGN PATENTS 1,274,486 9/ 1961 France.

I. TRAVIS BROWN, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,392,020 July 9, 1968 Henry C. Yutzy et al.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 34, "no not" should read do not Column 2, line 31, after "may be" insert a Column 12, line 8, "Wratten No. 48 lighter filter" should read Wratten N0. 47 light filter Column 18, line 8, "about" should read above Signed and sealed this 23rd day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr. WILLIAM E. JR.

Attesting Officer Commissioner of Patents 

